1. Field of the Invention
This invention relates generally to solar energy collection systems and more particularly to a new and improved solar tracking system for use therewith.
2. Description of the Prior Art
Despite the great need for a commercially acceptable system for collection and utilization of solar energy, there is no single mechanism, to the best of my knowledge, which satisfactorily fills all the requirements that such a system be a relatively low cost and low maintenance mechanism with high efficiency and dependability.
The prior art is replete with various mechanisms and systems which fall into three basic classes of solar energy collection systems and those classes are sometimes referred to as nontracking systems, single axis tracking systems and two axis tracking systems. Briefly, a nontracking solar collection system is a fixedly mounted structure, normally of planar configuration, which is positioned so that it faces in the general direction of the apparent diurnal path of the sun at an elevation determined by the geographic location. Solar radiation impinging on the surface of the nontracking collector heats a fluid medium, such as air or water, which is continuously passed through the collector. Such nontracking systems are relatively low cost dependable mechanisms due to the absence of a sun tracking capability, however, this same lack of a sun tracking capability places a limitation on the efficiency thereof. Typically, a nontracking solar collector system is capable of collecting about 17%-20% of the available solar radiation and can reach temperatures of between 300.degree.-400.degree. F.
A single axis solar collection system normally includes a solar radiation collector which is equipped to track the sun's apparent azimuthal path and is fixed at an elevation determined by the geographic location. The radiation collector, which is usually a reflecting and concentrating structure, reflectively focuses and concentrates the solar radiation on a solar energy absorber device through which the fluid medium is passed, and the absorber may be a fixedly mounted structure separate from the collector or may be supportingly carried thereon. Typical single axis solar collection systems are said to be capable of collecting about 30%-35% of the available solar radiation and can reach temperatures as high as 500.degree.-600.degree. F. Although significantly more efficient than a nontracking system, single axis systems are inherently more costly, require more maintenance, and are less dependable due to their configuration and the equipment needed to provide the sun tracking capability.
Two axis solar collection systems are similar to single axis systems in that they include a collector for reflecting and concentrating solar radiation on a solar energy absorber. However, as the name implies, two axis systems are equipped to track both the azimuth and elevation of the apparent diurnal cycle of the sun. Two axis solar collection systems are considerably more efficient than either of the other two basic classes of systems, and are reportedly capable of collecting as much as 75%-80% of the available solar radiation and are capable of reaching temperatures in the range of between 1000.degree.-2000.degree. F.
From the foregoing, it will be readily apparent that two axis solar energy collection systems are clearly superior. However, the superior performance of two axis systems, unfortunately, is not the only factor which determines which basic type of system will be selected. Such items as initial and operating costs, maintenance, dependability, and the like must be considered in that those items have had a major influence on the very slow public acceptance of solar energy systems in general and two axis systems in particular.
All of the individual structures and devices which make up a solar energy collection and utilization system will, of course, contribute to the costs, maintenance and dependability of such systems. In the single and two axis systems, the prior art tracking subsystem, i.e., the devices and components which sense the position of the sun and cause appropriate positioning of the solar energy collector, are comparatively high cost and high maintenance items.
In the early stages of the development of solar collection systems, and even some present-day systems, solar tracking was accomplished by clock and escapement mechanisms which operate through suitable gear trains.
With the development of sophisticated electronic equipment, the clock escapement type of tracking subsystems have been replaced, to a great extent by electronic systems. The electronic solar tracking subsystems normally utilize photocells in conjunction with suitable circuits for operation of collector positioning motors. In some subsystems, photoconductive cells are used and, as is well known, this type of photocell is efficient only at low temperatures and thus must be located remotely from the collector and shielded from the high temperatures of the collector. In other electronic solar tracking subsystems, photovoltaic cells are used which as known, produce a small voltage when light falls thereon. Since the voltages produced by photovoltaic cells are small and incapable of directly operating collector positioning equipment, they are used as triggering signals which operate comparatively complex circuitry, or other devices which in turn operate collector positioning equipment such as electric motors.
A typical prior art electronic solar tracking subsystem is discussed in U.S. Pat. No. 4,111,184. The prior art subsystem discussed in this Patent includes sun position sensors, such as the above described photovoltaic cells, which produce signals representative of the elevation and azimuth of the sun. A solar tracking position signal generator, comprising two potentiometers, the movable arms of which are positioned to represent the location of the collector in elevation and azimuth, produces two signals representative of the elevation and azimuth of the collector. The signals produced by the sun sensors and those produced by the signal generator are compared in subtracter devices one of which produces a difference signal that operates an elevation positioning motor, and the other of which produces a difference signal which operates an azimuth positioning motor.
It will now be seen that the prior art solar tracking subsystems are relatively delicate and sensitive structures as far as the sensors are concerned, and thus, must be protected and shielded from the damaging effects of the hostile environment in which solar systems operate. Further, those subsystems are relatively complex and therefore quite costly and require considerable maintenance.
Therefore, a need exists for a new and improved solar tracking subsystem, for use in solar collector systems, which overcomes some of the problems and shortcomings of the prior art.